Hydrocarbon recovery operations commonly allow reservoir gas within the formation to flow into the wellbore and to the surface with the liquid hydrocarbons. This practice initially drives high volumes of hydrocarbons into the well and up through the production tubing. Conventional hydrocarbon producing methods thus allow, and in many cases rely upon, the pressurized reservoir gases to directly assist in lifting the production fluids to the surface. This practice thus utilizes the pressure and liquid-driving capabilities of the reservoir gas to improve early well production recovery. While prevalent, this practice significantly reduces the ultimate recovery of liquid hydrocarbon reserves from the formation.
Liquid/gas separators have been used downhole in producing oil and gas wells to allow the entry of reservoir fluids which are in the liquid state into the tubular string that conveys the liquid fluids to the surface, and to prevent the entry of fluids in the gaseous state into the producing tubular string. One type of separation device, which remains immersed in the surrounding downhole fluid, includes a float and a valve arrangement. When this separation device is full of liquid, an open conduit is provided from the reservoir to the producing tubular. When the liquid is displaced by gas in the separation device, the float rises due to its increased buoyancy and a valve closes to prevent the entry of fluids into the producing tubular.
This separator thus includes a float activated valving system which opens when the separator is full of liquid and closes when that liquid is displaced by gas. The flotation system within this separator is configured to operate in the vertical or substantially vertical orientation. When the liquid/gas separator is open, the separator allows liquid to be transmitted by pressure energy within the producing formation upward through the tubular string which is positioned above a standing or check valve, and then to be lifted to the surface by a conventional pump powered by a reciprocating or rotating (progressive cavity) rod string. Other types of available downhole pumps, such as electrical submersible pumps or hydraulic (jet-type) pumps, may also be used to lift the liquid to the surface once it is entrapped above the liquid gas separator and within the production tubing string.
In practice, the downhole separator does little to cause or accelerate the separation of liquid and gas. Rather, the device senses the presence of a gas or a liquid within the device by the float, and allows only liquid entry into the production tubing string. The separator thus operates within a downhole well in a manner similar to a float operated valve controller which detects the liquid/gas interface within a surface vessel. One type of separation device marketed as the Korkele downhole separator has proven effective in many installations.
The separator may be placed and operated within a cased wellbore with a conventional diameter casing therein or may also be operated in an open hole. In either case, the separator may be suspended in the well from production tubing. The basic advantage of the Korkele downhole separator is that it improves performance of the well and the well-reservoir production system by allowing for the production of liquids only, i.e., it prevents the entry of gas from the reservoir into the production tubular string. The downhole separator as discussed above is more fully described in a July 1972 article in World Oil, pages 37-42. Further details with respect to this separator are disclosed in U.S. Pat. No. 3,643,740 granted to Kork E. Kelley and hereby incorporated by reference.
Other prior art includes U.S. Pat. Nos. 1,507,454 and 1,757,267. The '454 patent discloses an automatic pump control system with an upright stem connected to a diaphragm to operate a standing valve. The '267 patent discloses a gas/oil separator having a separating chamber located within the tubing and a mechanism for diverting the path of oil over an enlarged contact surface to separate free oil from gas.
U.S. Patents naming Kork Kelly as an inventor or co-inventor include U.S. Pat. Nos. 2,291,902; 3,410,217; 3,324,803; 3,363,581; and 3,451,477. The '902 patent discloses a gas anchor having a float connected to a valve stem which operates a valve head. The '217 patent discloses a separator for liquid control in gas wells. The '803 patent discloses a device having a floating bucket connected by a rod for liquid gas wells. A valve member is disclosed below and in close proximity to a check ball. The '581 patent discloses a pressure balanced and full-opening gas lift valve. The '477 patent relates to an improved method for effecting gas control in oil wells. The device includes a flotation bucket with an open top and a valve string including a valve member connected to the top of a rod, with the bottom of the rod connected to the bottom bucket. The '740 patent discloses both methods and apparatus for effecting gas control in oil wells utilizing a flotation bucket with an open top and a valve string including a valve member connected to the top of a rod. U.S. Pat. No. 3,971,213 discloses an improved pneumatic beam pumping unit.
U.S. Pat. No. 3,408,949 discloses a bottom hole gas/liquid separator having a float tube encircling the lower end of a production tubing and adapted to move vertically within a housing. A production valve is disposed on the upper end of a space bar such that the float tube and spacer bar form a sand trap. U.S. Pat. No. 3,483,827 discloses a well producing device which utilizes a gas separator in a tubing string to separate liquid from gas prior to entry into a downhole pump. U.S. Pat. No. 3,724,486 discloses a liquid and gas separation device for a downhole well wherein a valve member is moveable and resiliently mounted on a moveable liquid container designed so that liquid will accumulate within the bore hole above the position where gas enters to decrease or prohibit the entry of gas into the bore hole. U.S. Pat. No. 3,993,129 discloses a fluid injection valve for use in well tubing for controlling the flow of fluid between the outside of the production tubing and the inside of the tubing.
More recently issued patents include U.S. Pat. Nos. 4,474,234 and 4,570,718. The '234 patent discloses a hydrocarbon production well having a safety valve removably mounted in the production tubing beneath a pump. The '718 patent relates to an oil level sensor system and method for operating an oil well whereby upper and lower oil well sensors control pumping of the well. U.S. Pat. No. 5,456,318 discloses a fluid pumping device having a fluid inlet valve disposed at its lower end for fluid flow into the body of the device, a plunger assembly disposed in the interior of the body for reciprocating movement, a seal which cooperates with the plunger assembly to divide the body into isolated upper and lower chambers and to divide the body from the production tube, and fluid flow control valves.
U.S. Pat. No. 5,653,286 discloses a downhole gas separator connected to the lower end of a tubing string designed such that primary liquid fluid flows into a chamber within the separator. U.S. Pat. No. 5,655,604 discloses a downhole production pump and circulating system which utilizes valves wherein the valve balls are attached to projector stems. U.S. Pat. No. 5,664,628 discloses an improved filter medium for use in subterranean wells.
None of the prior art discussed above fully benefits from the capability of an effective downhole liquid/gas separator. Further improvements are required to obtain the significant advantages realized by retaining within the downhole producing formation the inherent energy, i.e. the compressed gas, which drives the desired hydrocarbon products from the reservoir rock and into the wellbore so that they may be more efficiently produced. By preventing the formation gas at bottom of the well from entering the production tubing string and permitting only the entry of liquids into the tubing string, the retained potential energy and expansive properties of the gas may be effectively utilized to produce a higher percentage of liquid reserves than would otherwise be recovered by conventional technology. Alternatively, improved procedures for pumping liquid accumulations off gas wells are necessary to improve the performance of gas wells. Moreover, further improvements in a separation device, in methods of using a separation device, and in the configuration and operation of the overall hydrocarbon recovery system in which a separation device is employed are required to benefit from the numerous applications in which such a device may be effectively used to enhance recovery of hydrocarbons.
The disadvantages of the prior art are overcome by the present invention. An improved separation device, a method of operating a separation device, an improved overall hydrocarbon recovery system, and improved techniques for recovering hydrocarbons are hereinafter disclosed.